A hydrofoil vessel

ABSTRACT

The invention involves a hydrofoil vessel ( 1 ) comprising a hydrofoil assembly ( 4 ), and a hull assembly ( 2 ) presenting, when the vessel is floating at rest, a vertical symmetry plane (SP), wherein the hydrofoil assembly ( 4 ) comprises two struts ( 401 ) extending from the hull assembly ( 2 ) on opposite transverse sides of the symmetry plane (SP), mainly downwards when the vessel is floating at rest, or mainly partly away from the symmetry plane and partly downwards when the vessel is floating at rest, wherein the hydrofoil assembly ( 4 ) comprises two main foil portions ( 411 ) each extending from a respective one of the struts ( 401 ), at least partly towards the symmetry plane (SP), wherein each strut ( 401 ) comprises a strut foil ( 402 ) with a non-symmetrical cross-section, and with a pressure side ( 402 P) facing at least partly towards the symmetry plane, and a suction side ( 402 S) facing at least partly away from the symmetry plane (SP).

TECHNICAL FIELD

The invention relates to a hydrofoil vessel comprising a hydrofoil assembly, and a hull assembly presenting, when the vessel is floating at rest, a vertical symmetry plane. The invention also relates to a hydrofoil set for a hydrofoil vessel.

BACKGROUND

In the field of hydrofoil vessels, there has traditionally been two types of hydrofoils. One of them is a submerged, or immersed hydrofoil, i.e. a foil that is designed to be fully submerged during a cruising mode of the vessel. An immersed foil may have an adjustable pitch orientation so as to change the angle of attack of the adjustable hydrofoil. The other hydrofoil type is a surface piercing hydrofoil.

A known problem with hydrofoil vessels is that the vessel may lean outwards in turns, and be difficult to operate in high seas. This is the case with both submerged and surface piercing hydrofoils. In a hydrofoil vessel with an immersed foil the inherent lack of roll stability creates a challenge. Roll may be defined as a movement around a roll axis which is substantially parallel to a direction of forward travel of the vessel. The roll axis could extend within the hull assembly symmetry plane, and it could be substantially horizontal. Where the hull assembly comprises a single hull, the roll movement could be a movement around an axis which extends from the bow to the stern of the hull. An immersed hydrofoil may, for the roll stability, be arranged to be controlled so as to present different lift coefficients, and/or different angles of attack, along the length of the foil, e.g. as described in SE540588C2.

However, there is nevertheless a desire to achieve a good roll stability of hydrofoil vessels.

SUMMARY

An object of the invention is to improve the roll stability of a hydrofoil vessel.

The object is achieved with a hydrofoil vessel according to claim 1. Thus, the invention provides a hydrofoil vessel comprising a hydrofoil assembly. The vessel comprises a hull assembly presenting, when the vessel is floating at rest, a vertical symmetry plane. The hydrofoil assembly comprises two struts extending from the hull assembly on opposite transverse sides of the symmetry plane, mainly downwards when the vessel is floating at rest, or mainly partly away from the symmetry plane and partly downwards when the vessel is floating at rest. Each strut comprises a strut foil with a non-symmetrical cross-section, and with a pressure side facing at least partly towards the symmetry plane, and a suction side facing at least partly away from the symmetry plane. The hydrofoil assembly comprises two main foil portions each extending from a respective one of the struts, at least partly towards the symmetry plane.

In embodiments of the invention, the hydrofoil vessel may be a hydrofoil boat. The hull assembly may comprise a single hull. In some embodiments, the hull vessel may comprise a multihull assembly. For example, the vessel may have catamaran or a trimaran hulls. The vertical symmetry plane may be imaginary. The external shape of the hull assembly, or at least major features thereof, may be mirrored with reference to the symmetry plane.

Where the struts extend mainly downwards when the vessel is floating at rest, the struts may extend mainly within a respective plane which is parallel to the symmetry plane.

The strut foils and the main foil portions may be surface piercing. For this, the main foil portions may have cross-sectional shapes, orientations, and dimensions, adapted to minimize or avoid air being sucked down when the main foil portions are under the water surface, in particular under but close to the water surface, or at the surface. However, in some embodiment the main foil portions may be submerged.

The positions where the main foils extend from the struts are below the respective positions where the struts extend from the hull assembly. In some embodiments, each main foil portion extends from a distal end of the respective strut. Thereby, the main foil portions may extend inwards from distal ends of the respective struts. In some embodiments however, each main foil portion extends from a position of the respective strut which is above the distal end of the respective strut. Thereby, the main foil portions may be connected to the respective struts at a distance from the distal ends of the struts. Each main foil portion may extend inside and/or below the respective strut. Each main foil portion may extend at least partly below the respective strut, where the respective strut extends partly outwards and partly downwards. The main foil portions may be located below the hull assembly when the vessel is floating at rest.

In some embodiments, the hydrofoil assembly comprises main foil parts that extend from the respective struts away from the symmetry plane. Such main foil parts may be extensions of said respective main foil portions extending at least partly towards the symmetry plane. The main foil parts may be cantilevered foil portions which form with the main foil portions a single main foil.

The struts may extend substantially within a respective plane which is parallel to the symmetry plane. The struts may extend downwards when the vessel is floating at rest, substantially within the respective plane which is parallel to the symmetry plane. In some embodiments, a main extension of the struts may be partly away from the symmetry plane and partly downwards when the vessel is floating at rest. In other embodiments, a main extension of the struts may be partly towards the symmetry plane and partly downwards when the vessel is floating at rest. Nevertheless, preferably, the extension of each strut is such that a vector of the resultant hydrodynamic force acting on the strut, has a direction away from the symmetry plane, under the center of gravity of the vessel.

The strut foils may form the respective struts, or the strut foils may form parts of the respective struts. Preferably, the length of each strut foil is at least 50%, at least 70%, at least 80%, or at least 90%, of the length of the respective strut. The non-symmetrical cross-section of each strut foil may extend substantially fore and aft in relation to the vessel. The strut foil pressure sides may face at least partly inwards in relation to the hull assembly. The strut foil suction sides may face at least partly outwards in relation to the hull assembly.

The asymmetry of the strut foils creates, when the vessel heels over, a lift force directed at least partly outwards from the vessel, and in some embodiments partly upwards. The force causes a righting moment, thereby providing roll stabilization, e.g. in rough conditions.

More specifically, by the struts extending from the hull assembly on opposite transverse sides of the symmetry plane, mainly within a respective plane which is parallel to the symmetry plane, or partly away from the symmetry plane and partly downwards when the vessel is floating at rest, and by each strut foil having a non-symmetrical cross-section a pressure side facing towards the symmetry plane, and a suction side facing away from the symmetry plane, it is ensured that the strut foils provides a force in relation to the center of gravity of the vessel, that serves to roll the vessel in a direction which opposes heeling of the vessel. Particularly, the strut foils may serve to provide a smallest angle between a resultant hydrodynamic force acting on one of the strut foils, and a vector from the center of gravity of the vessel to a center of pressure of the hydrodynamic force, which angle serves to rotate the vessel in a direction which is opposite to a heeling direction of the vessel. Said angle may be equal to or greater than 10 degrees, equal to or greater than 20 degrees, equal to or greater than 30 degrees, equal to or greater than 40 degrees, or equal to or greater than 50 degrees. The center of pressure of the hydrodynamic force may also be referred to as the point of attack of the hydrodynamic force.

It should be noted that in some embodiments, the hydrofoil assembly may comprise one or more additional struts. The additional struts may have non-symmetrical cross-sections, similarly to the struts described above, or the additional struts may have symmetrical cross-sections.

Preferably, each strut further comprises a major portion and a transition portion, the transition portion forming a transition from the major portion to the respective main foil portion, wherein the length of the transition portion is no more than 30%, no more than 20%, no more than 10%, or no more than 5%, of the length of the respective strut. The length of the transition portion may be defined by the length of a trailing edge thereof. The length of the strut may be defined by the length of a trailing edge thereof. The major portion of the respective strut and the transition portion may form parts of the strut, and the transition portion may be located between the major portion and the respective main foil portion.

By the transition portion, sharp corners between the struts and the main foil portions may be avoided. Sharp corners may otherwise create a need for reinforcements to avoid structural damage. A structurally beneficial arrangement may thereby be provided, while the hydrodynamic features improving roll stability, are retained. As understood, features contributing to the roll stability include the struts extending mainly within a respective plane which is parallel to the symmetry plane, or mainly partly away from the symmetry plane and partly downwards when the vessel is floating at rest, and each strut foil having a non-symmetrical cross-section, a pressure side facing towards the symmetry plane, and a suction side facing away from the symmetry plane. Each strut foil may be formed by a respective strut major portion or a part thereof.

The transition portion may be provided at, or form, a distal end of the respective strut. The transition portion may be provided as a bend from the strut major portion to the main foil portion. The transition portion may form a smooth transition from the strut major portion to the main foil portion. Specifically, the transition portion may have a radius to form such a smooth transition. Alternatively, the transition portion may have a straight part, or it may be entirely straight.

In some embodiments, each main foil portion extends to the other of the main foil portions. Thereby, the main foil portions may form together a main foil. The main foil may extend from one strut to the other of the struts.

Each main foil portion extending to the other of the main foil portions allows a simple integration of the main foil assembly with the hull assembly, since the main foil assembly may be connected to the hull assembly only by the struts. Nevertheless, in some embodiments, each main foil portion extends from a respective of the struts to the hull assembly.

The hull assembly may present, when the vessel is floating at rest, a horizontal plane coinciding with a waterline of the hull assembly. The horizontal plane may be imaginary. The horizontal plane may coincide with the waterline of the hull assembly when the vessel is floating at rest.

In some embodiments, the main foil portions may extend towards the symmetry plane and substantially in parallel with the horizontal plane. Thereby the main foil may be horizontal when the vessel is at rest. Thereby, the manufacturing of the main foil may be relatively simple.

However, in some embodiments, the main foils may extend from the respective strut, partly towards the symmetry plane and partly towards the horizontal plane. By such extensions, partly towards the symmetry plane and partly upwards, the main foil portions may be inclined when the vessel is at rest. Thereby, the main foil may present the shape of an inverted V. In further embodiments, the main foils may extend from the respective strut, partly towards the symmetry plane and partly away from the horizontal plane.

In some embodiment, two main foil portions each extending from a respective one of the struts, wherein inner parts of the main foil portions extend towards the symmetry plane and substantially in parallel with the horizontal plane, and outer parts of the main foil portions extend partly towards the symmetry plane SP and partly towards the horizontal plane. Thereby, each main foil portion may present an outer inclined part, and an inner horizontal part.

Thus, the main foil portions may each extend from a respective one of the struts, towards the symmetry plane and substantially in parallel with the horizontal plane, and/or partly towards the symmetry plane and partly towards the horizontal plane.

Each main foil portion may have a non-symmetrical cross-section, and a pressure side facing at least partly away from the horizontal plane, and a suction side facing at least partly towards the horizontal plane. Thereby, the pressure side of each main foil portion may face at least partly downwards when the vessel is floating at rest, and the suction side may face at least partly upwards when the vessel is floating at rest. The non-symmetrical cross-section of each main foil portion may extend substantially fore and aft in relation to the vessel.

Each main foil portion extending from a respective of the struts, towards the symmetry plane and substantially in parallel with the horizontal plane, or partly towards the symmetry plane and partly towards the horizontal plane, and each main foil portion having a non-symmetrical cross-section, and a pressure side facing at least partly away from the horizontal plane, and a suction side facing at least partly towards the horizontal plane, provides an additional force in relation to the center of gravity of the vessel, that serves to roll the vessel in the direction which is opposite to the heeling direction of the vessel. Particularly, the main foil portions may serve to provide a smallest angle between a resultant hydrodynamic force acting on one of the main foils, and a vector from the center of gravity of the vessel to a center of pressure of the hydrodynamic force, which angle serves to rotate the vessel in a direction which is opposite to a heeling direction of the vessel. Said angle may be equal to or greater than 10 degrees, equal to or greater than 20 degrees, equal to or greater than 30 degrees, equal to or greater than 40 degrees, or equal to or greater than 50 degrees.

Thereby, through the combined hydrodynamic contributions of the strut foils and the mail foil portions, a particularly high roll stabilization of the vessel may be provided.

In embodiments where the main foil portions extend from a respective one of the struts, partly towards the symmetry plane and partly towards the horizontal plane, the inclination of the main foil portions may serve to provide a beneficial angle between a resultant hydrodynamic force acting on one of the main foil portions, and a vector from the center of gravity of the vessel to a center of pressure of the hydrodynamic force. More specifically, by the inclination of the main foil portions, the hydrodynamic force acting on one of the main foil portions may be brought closer to being perpendicular to the vector from the center of gravity of the vessel to the center of pressure of the hydrodynamic force. Thereby, the vessel righting effect of the force may be high.

Nevertheless, as suggested, in some embodiments, the main foil portions each extend from a respective one of the struts, partly towards the symmetry plane and partly away from the horizontal plane. Thereby, the main foil may present the shape of V.

Preferably, the strut foils each extend substantially within a respective plane which is parallel to the symmetry plane. Thereby, the struts, or at least the strut foils thereof, may extend vertically as seen in the direction of travel of the vessel. In a side view of the vessel, the struts, or at least the strut foils thereof, may extend vertically, or in a non-zero angle to a vertical direction.

Where the struts, or at least the strut foils thereof, extend substantially within a respective plane which is parallel to the symmetry plane, the hydrofoil assembly may be relatively simple to manufacture, in particular where the main foil portions extend substantially in parallel with the horizontal plane. The struts may be fixed to the hull assembly at lateral edges thereof. Thereby the hydrofoil assembly may have a horizontal main part formed by the main foil, and two vertical parts, formed by the struts, connecting the horizontal part with the hull assembly.

Preferably, the strut foils and the main foil portions are fixed in relation to the hull assembly. The strut foils and main foil portions are preferably surface piercing foil. Thereby, the strut foils and main foil portions can go in and out of the water without sucking down air and loose lift.

Preferably, the vessel comprises, in addition to the hydrofoil assembly, an adjustable hydrofoil having an adjustable pitch orientation so as to change the angle of attack of the adjustable hydrofoil. The adjustable hydrofoil may be, compared to the hydrofoil assembly, further away from the horizontal plane. The adjustable hydrofoil may be, when the vessel is floating at rest, below the hydrofoil assembly.

The adjustable hydrofoil may be arranged to be submerged at speeds when the hull assembly is lifted out of the water. At such speeds also the hydrofoil assembly may be lifted out of the water. The angle of attack control allows control of the vertical position of the adjustable hydrofoil. The adjustable hydrofoil may, for the roll stability, be arranged to be controlled so as to present different lift coefficients, and/or different angles of attack, along the length of the adjustable hydrofoil foil.

Problems with known hydrofoils include a submerged foil typically being most efficient within a rather small speed range, due to the need to provide a compromise between a good take-off performance and a good cruising performance. Another disadvantage with a submerged hydrofoil is that it can lose lift in high seas due to ventilation, causing the vessel to suddenly drop down. A surface piercing hydrofoil has a problem of an overall low efficiency.

In embodiments of the invention, the main foil portions will provide, in addition to the adjustable hydrofoil, a lifting force at relatively low speeds of the vessel. This will allow for a relatively small propulsive force, and hence a relatively small engine or motor, for taking off from a hull displacement state of the vessel, to a foil carried state. In addition, or alternatively, the adjustable hydrofoil may be made relatively small, and hence more efficient at relatively high speeds. Furthermore, the main foil portions will allow for the vessel to be supported in rough sea by giving it extra lift when the hull assembly tends to fall down into the water. In addition, a slow speed rough sea mode is made possible, where the vessel runs on the adjustable hydrofoil and the main foil portions, with the hull assembly relatively close to the water.

Thereby, a hydrofoil vessel may be provided with a combination of an immersed foil, and a further foil, achieving, while combining a good high speed performance with a good take-off and high seas performance, a good roll stability of the vessel.

The adjustable hydrofoil may be connected to the hull assembly independently of the hydrofoil assembly, by means of one or more foil holding members. This simplifies the production of the hydrofoil vessel.

The hydrofoil vessel may be such that it is not adapted to be driven by wind power. For example, the vessel may be a power boat.

The object is also reached with a hydrofoil set according to claim 11, the hydrofoil set comprising the hydrofoil assembly. In some embodiments, the hydrofoil set is identical to the hydrofoil assembly. In other embodiments, the hydrofoil assembly forms a subset of the hydrofoil set. Where the hydrofoil set also comprises the adjustable hydrofoil, the adjustable hydrofoil may be adapted to be connected to the hull assembly by means of the one or more foil holding members.

Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, embodiments of the invention will be described with reference to the drawings, in which:

FIG. 1 shows a perspective view a hydrofoil vessel according to an embodiment of the invention,

FIG. 2 shows a side view of the vessel in FIG. 1 ,

FIG. 3 shows a view of the vessel in FIG. 1 from in front of the vessel,

FIG. 4 shows a cross-sectional view with the section oriented as indicated by the arrows IV in FIG. 2 ,

FIG. 5 shows a detail in FIG. 3 ,

FIG. 6 shows the view of FIG. 3 , when the vessel is heeling over,

FIG. 7 shows a hydrofoil vessel according to an alternative embodiment of the invention, in a view corresponding to the view in FIG. 3 ,

FIG. 8 shows a hydrofoil vessel according to a further alternative embodiment of the invention, in a view corresponding to the view in FIG. 3 ,

FIG. 9 shows a hydrofoil vessel according to another embodiment of the invention, in a view corresponding to the view in FIG. 3 ,

FIG. 10 shows a hydrofoil vessel according to a further embodiment of the invention, in a view corresponding to the view in FIG. 3 ,

FIG. 11 shows a hydrofoil vessel according to a yet another embodiment of the invention, in a view corresponding to the view in FIG. 3 , and

FIG. 12 shows a hydrofoil vessel according to a further embodiment of the invention, in a view corresponding to the view in FIG. 3 .

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 1 and FIG. 2 show a hydrofoil vessel 1. The vessel comprises a hull assembly 2 comprising a single hull.

Reference is made also to FIG. 3 . The hull assembly 2 presents, when the vessel is floating at rest, an imaginary vertical symmetry plane SP, and an imaginary horizontal plane HP coinciding with a waterline of the hull assembly 2.

The vessel comprises an adjustable hydrofoil 301 having an adjustable pitch orientation so as to change the angle of attack of the adjustable hydrofoil. The adjustable hydrofoil 301 is connected to the hull assembly by means of two foil holding members 302. The adjustable hydrofoil 301 may be, as exemplified in FIG. 2 , in the direction of travel of the vessel 1, located substantially at a center of gravity CG of the vessel.

The vessel also comprises a propulsion arrangement. The propulsion arrangement comprises a propeller 501. The propulsion arrangement is provided at a stern of the hull. In this example, the propulsion arrangement comprises an electric motor in a pod 502. The motor is arranged to drive the propeller, which is mounted on the pod. The pod is mounted to the hull assembly via a pod carrying element 503. The motor is arranged to be powered by a power source such as a battery pack 504. The propulsion arrangement may be controlled so as to steer the vessel.

The vessel could be provided with any suitable alternative propulsion arrangement, e.g. comprising an outboard or an inboard engine.

The vessel further comprises an aft foil 601. The aft foil is arranged to support, in a hydrofoil driving mode, an aft part of the hull assembly. The aft foil is mounted to the hull assembly via an aft foil carrying element 503. In this embodiment, the aft foil carrying element is also the pod carrying element.

The vessel further comprises a hydrofoil assembly 4. As exemplified in FIG. 3 , the adjustable hydrofoil 301 is, compared to the hydrofoil assembly, further away from the horizontal plane HP. As exemplified in FIG. 2 , the hydrofoil assembly 4 may be, in the direction of forward travel of the vessel 1, located further forward than the adjustable hydrofoil 301. Alternatively, the hydrofoil assembly 4 may be located behind the adjustable hydrofoil 301. As a further alternative, the hydrofoil assembly 4 and the adjustable hydrofoil 301 may be in substantially the same position in the direction of travel of the vessel 1.

The hydrofoil assembly 4 comprises two struts 401 extending from the hull assembly 2 on opposite transverse sides of the symmetry plane SP, mainly within a respective plane which is parallel to the symmetry plane. Each strut 401 comprises a strut foil 402.

As exemplified in FIG. 4 , each strut foil 402 has a non-symmetrical cross-section, and with a suction side 402S facing away from the symmetry plane SP, and a pressure side 402P facing towards the symmetry plane.

The hydrofoil assembly 4 comprises two main foil portions 411 each extending from a respective of the struts 401, towards the symmetry plane SP and substantially in parallel with the horizontal plane HP. Each main foil portion 411 extends to the other of the main foil portions 411. The main foil portions 411 form together a single main foil.

Each main foil portion 411 has a non-symmetrical cross-section, and a pressure side 411P facing downwards when the vessel is floating at rest, and a suction side 411S facing upwards when the vessel is floating at rest.

The strut foils 402 and the main foil portions 411 are fixed in relation to the hull assembly 2. The strut foils 402 and the main foil portions 411 are surface piercing. In some embodiments, the strut foils 402 and/or the main foil portions 411 may be adjustable and/or retractable.

Reference is made also to FIG. 5 . Each strut 401 further comprises a major portion 403 and a transition portion 404. The transition portion forms a transition from the major portion to the respective main foil portion 411. The transition portion 404 is provided as a bend from the major portion 403 to the main foil portion 411. The transition portion forms a smooth transition from the major portion to the main foil portion. The length Ltp of the transition portion 404 is preferably no more than 30% of the length Ls of the respective strut. In the example in FIG. 1 - FIG. 5 , the length Ltp of each transition portion 404 is about 10% of the length Ls of the respective strut. A trailing edge TE of the hydrofoil assembly is indicated with a broken line in FIG. 5 . The length Ltp of the transition portion may be defined by the length of a trailing edge thereof. The length Ls of the strut may be defined by the length of a trailing edge thereof.

The adjustable hydrofoil 301 is in the embodiment in FIG. 1 - FIG. 4 connected to the hull assembly, independently of the hydrofoil assembly 4, by means of the two foil holding members 302. In alternative embodiments, the adjustable hydrofoil 301 may be mounted to the hydrofoil assembly 4, by means of the one, or more than two, foil holding members 302.

Reference is made also to FIG. 6 . When the vessel is not heeling over, the strut foils 402 may be, depending on the speed of the vessel, above the water, or partly submerged in the water. When the vessel heels over, one of the strut foils 402 becomes lower than the other of the strut foils. Thereby, the lower strut foil may be further submerged in water than the higher strut foil. The lower strut foil may be partly or fully submerged in the water while the higher strut foil may be less submerged than the lower strut foil, or above the water. Thereby, the hydrodynamic force will be larger on the lower strut foil than on the higher strut foil.

The orientation of the lower of the strut foils serves to provide a smallest angle AS 1 between a resultant hydrodynamic force F1 acting on the lower strut foil, and a vector V1 from the center of gravity CG of the vessel to a center of pressure of the hydrodynamic force F1, which is at least 10 degrees, in this example 29 degrees. Thereby, the force F1 will counteract the heeling of the vessel.

Further, when the vessel heels over, one of the main foil portions 411 becomes lower than the other of the main foil portions. Thereby, the lower main foil portion may be further submerged in water than the higher main foil portion. The lower main foil portion may the partly or fully submerged in the water while the higher main foil portion may be less submerged than the lower main foil portion, or above the water. Thereby, the hydrodynamic force will be larger on the lower main foil portion than on the higher main foil portion.

The orientation of the lower of the main foils portion serves to provide a smallest angle AS2 between a resultant hydrodynamic force F2 acting on the lower main foil portion, and a vector V2 from the center of gravity CG of the vessel to a center of pressure of the hydrodynamic force F2, which is at least 10 degrees, in this example 32 degrees. Thereby, the force F2 will also counteract the heeling of the vessel.

FIG. 7 shows an alternative embodiment, which is similar to the embodiment shown in FIG. 1 - FIG. 6 , except for the following features: Outer parts of the main foil portions 411 each extend from a respective one of the struts 401, towards the symmetry plane and partly upwards when the vessel is floating at rest. Inner parts of the main foil portions 411 each extend towards the symmetry plane SP and substantially in parallel with the horizontal plane HP. The outer parts of each main foil portion 411 has a pressure side 411P facing partly downwards when the vessel is floating at rest, and a suction side 411S facing partly upwards when the vessel is floating at rest. The inner parts of each main foil portion 411 has a pressure side 411P facing downwards when the vessel is floating at rest, and a suction side 411S facing upwards when the vessel is floating at rest.

FIG. 8 shows a further alternative embodiment, which is similar to the embodiment shown in FIG. 1 - FIG. 6 , except for the following features: The main foil portions 411 each extend from a respective one of the struts 401, towards the symmetry plane and partly upwards when the vessel is floating at rest. Each main foil portion 411 extends to the hull assembly 2. Thereby, the main foil portions may be mounted to the hull assembly. Each main foil portion 411 has a pressure side 411P facing partly downwards when the vessel is floating at rest, and a suction side 411S facing partly upwards when the vessel is floating at rest.

FIG. 9 shows a further alternative embodiment, which is similar to the embodiment shown in FIG. 1 - FIG. 6 , except for the following features: The struts 401 extend from the hull assembly 2 on opposite transverse sides of the symmetry plane SP, mainly partly away from the symmetry plane and partly downwards when the vessel is floating at rest. Thereby, the strut foil pressure sides 402P face partly towards the symmetry plane SP, and the strut foil suction sides 402S face partly away from the symmetry plane SP.

FIG. 10 shows another embodiment, which is similar to the embodiment shown in FIG. 1 -FIG. 6 , except for the following: The vessel does not comprise an adjustable hydrofoil. The vessel comprises a surface piercing hydrofoil assembly.

FIG. 11 shows yet another embodiment. The vessel comprises a hydrofoil assembly comprising two struts 401 extending from the hull assembly on opposite transverse sides of the symmetry plane SP, mainly within a respective plane which is parallel to the symmetry plane. Each strut 401 comprises a strut foil 402. Each strut foil 402 has a non-symmetrical cross-section, and with a suction side 402S facing away from the symmetry plane SP, and a pressure side 402P facing towards the symmetry plane.

The hydrofoil assembly 4 comprises two main foil portions 411 each extending from a respective of the struts 401, towards the symmetry plane SP and substantially in parallel with the horizontal plane HP. Each main foil portion 411 extends to the other of the main foil portions 411.

Cantilevered foil portions 412 each extend from a respective of the struts 401, away from the symmetry plane SP. The cantilevered foil portions 412 extend substantially in parallel with the horizontal plane HP. The main foil portions 411 and the cantilevered foil portions 412 form together a single main foil. The main foil has a non-symmetrical cross-section, and a pressure side facing downwards when the vessel is floating at rest, and a suction side 411S facing upwards when the vessel is floating at rest. The main foil has an adjustable pitch orientation so as to change the angle of attack of the adjustable hydrofoil. The main foil is an immersed hydrofoil.

FIG. 12 shows a further alternative embodiment, which is similar to the embodiment shown in FIG. 1 - FIG. 6 , except for the following features: The struts 401 extend from the hull assembly 2 on opposite transverse sides of the symmetry plane SP, mainly partly towards the symmetry plane and partly downwards when the vessel is floating at rest. Thereby, the strut foil pressure sides 402P face partly towards the symmetry plane SP, and the strut foil suction sides 402S face partly away from the symmetry plane SP. Further, the main foil portions 411 each extend partly towards the symmetry plane and partly away from the horizontal plane HP.

It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. 

1. A hydrofoil vessel comprising a hydrofoil assembly, and a hull assembly presenting, when the vessel is floating at rest, a vertical symmetry plane, wherein the hydrofoil assembly comprises two struts extending from the hull assembly on opposite transverse sides of the symmetry plane (SP), mainly downwards when the vessel is floating at rest, mainly partly away from the symmetry plane and partly downwards when the vessel is floating at rest, or mainly partly towards the symmetry plane and partly downwards when the vessel is floating at rest, wherein the hydrofoil assembly comprises two main foil portions each extending from a respective one of the struts, at least partly towards the symmetry plane (SP), wherein each strut comprises a strut foil with a non-symmetrical cross-section, and with a pressure side facing at least partly towards the symmetry plane, and a suction side facing at least partly away from the symmetry plane (SP).
 2. A hydrofoil vessel according to claim 1, wherein each strut comprises a major portion and a transition portion, the transition portion forming a transition from the major portion to the respective main foil portion, wherein the length of the transition portion is no more than 30% of the length of the respective strut.
 3. A hydrofoil vessel according to claim 1, wherein each main foil portion extends to the other of the main foil portions.
 4. A hydrofoil vessel according to claim 1, wherein the hull assembly presents, when the vessel is floating at rest, a horizontal plane (HP) coinciding with a waterline of the hull assembly, wherein the main foil portions extend substantially in parallel with the horizontal plane (HP).
 5. A hydrofoil vessel according to claim 1, wherein the hull assembly presents, when the vessel is floating at rest, a horizontal plane (HP) coinciding with a waterline of the hull assembly, wherein the main foil portions each extend partly towards the symmetry plane and partly towards the horizontal plane (HP).
 6. A hydrofoil vessel according to claim 1, wherein the hull assembly presents, when the vessel is floating at rest, a horizontal plane (HP) coinciding with a waterline of the hull assembly, wherein each main foil portion has a non-symmetrical cross-section, and a pressure side facing at least partly away from the horizontal plane (HP), and a suction side-facing at least partly towards the horizontal plane (HP).
 7. A hydrofoil vessel according to claim 1, wherein the strut foils each extend substantially within a respective plane which is parallel to the symmetry plane (SP).
 8. A hydrofoil vessel according to claim 1, wherein the strut foils and the main foil portions are fixed in relation to the hull assembly.
 9. A hydrofoil vessel according to claim 1, wherein the strut foils and the main foil portions are surface piercing.
 10. A hydrofoil vessel according to claim 1, wherein the vessel comprises, in addition to the hydrofoil assembly-, an adjustable hydrofoil having an adjustable pitch orientation so as to change the angle of attack of the adjustable hydrofoil.
 11. A hydrofoil vessel according to claim 10, wherein the hull assembly presents, when the vessel is floating at rest, a horizontal plane (HP) coinciding with a waterline of the hull assembly, wherein the adjustable hydrofoil-is, compared to the hydrofoil assembly, further away from the horizontal plane (HP).
 12. A hydrofoil vessel according to claim 10, wherein the adjustable hydrofoil is connected to the hull assembly independently of the hydrofoil assembly, by means of one or more foil holding members.
 13. A hydrofoil vessel according to claim 1, wherein the vessel is not adapted to be driven by wind power.
 14. A hydrofoil set for a hydrofoil vessel-comprising a hull assembly presenting, when the vessel is floating at rest, a vertical symmetry plane (SP), the hydrofoil set comprising a hydrofoil assembly comprising two struts adapted to extend from the hull assembly on opposite transverse sides of the symmetry plane (SP), mainly downwards when the vessel is floating at rest, mainly partly away from the symmetry plane and partly downwards when the vessel is floating at rest, or mainly partly towards the symmetry plane and partly downwards when the vessel is floating at rest, wherein the hydrofoil assembly comprises two main foil portions each adapted to extend from a respective one of the struts, at least partly towards the symmetry plane (SP), wherein each strut comprises a strut foil with a non-symmetrical cross-section, and with a pressure side adapted to face at least partly towards the symmetry plane, and a suction side-adapted to face at least partly away from the symmetry plane (SP). 